DESCRIPTION (Applicant's abstract): The goal of this project is to identify specific molecular steps that occur in vivo during establishment of colorectal cancer metastases to the liver. The proposed experimental approach will utilize intravital light and fluorescent video microscopy, a mouse xenograft model of human hepatic colorectal cancer metastases, fluorescent probes and two well-characterized colon cancer cell lines with high (CX1) and low (MIP-101) metastatic potential, and corresponding high and lack of expression of CEA, to visualize directly cell interactions during the development of liver metastases. Specific Aim 1 will document the initial in vivo sequence of interactions between circulating colon cancer cells and resident liver Kupffer cells in a live mouse model. These studies will compare the ability of highly (CX1) and poorly (MIP-101) metastatic human colon cancer cells to interact with and activate periportal Kupffer cells in vivo, and investigate whether pharmacological inhibition of Kupffer cells (with Gadolimium chloride) abrogates initiation of the metastatic cascade. Specific Aim 2 will document the in vivo location and sequence of cellular interactions from the onset of sinusoidal E-selectin expression to tumor cell adhesion, transmigration and colonization. These studies will document the sites and relative intensity of downstream sinusoidal and outflow venous endothelial cell E-selectin expression in vivo and correlate this with sites and the temporal sequence of tumor cell adherence, transmigration, and onset of metastatic tumor growth. Finally, since intravital microscopy is able to delineate in our tumor model the earliest onset of angiogenesis, we will correlate the onset of angiogenesis with tumor cell type and the timing and intensity of systemic macrophage recruitment. This project will allow identification of a series of in vivo steps that can be used to explore novel diagnostic and therapeutic probes in animal studies.